Process of drilling a well with a drilling fluid containing a starch product



Dec- 27, 1966 R. o. STEARNS ETAL 3,

PROCESS OF DRILLING A WELL WITH A DRILLING FLUID CONTAINING A STARCHPRODUCT Onginal Flled Aprll 10 1963 205527 0. SZEAP/VS QO/VALD J. l/lf/A fe/77' wvavme! United States Patent Ofiice 3,294,681 Patented Dec.27, 1966 3,294,681 PROCESS OF DRILLING A WELL WITH A DRILL- ING FLUIDCONTAINING A STARCH PRODUCT Robert 0. Stearns, Barstow, Calif., andDonald J. Weintritt, Houston, TeX., assignors to National Lead Company,New York, N.Y., a corporation of New Jersey Original application Apr.10, 1963, Ser. No. 272,103, now Patent No. 3,256,115, dated June 14,1966. Divided and this application Oct. 21, 1965, Ser. No. 499,644 3Claims. (Cl. 252-85) This application is a division of our co-pendingapplication Ser. No. 272,103, filed April 10, 1963, now US. Patent No.3,256,115.

This invention relates to the preparation of a pregelatinized starchymaterial, such as starch or a starchy flour, in order to produce amaterial dispersible in cold water and resistant to microbiologicaldegradation.

In many fields of use of starch or starchy flour, it is necessary thatthe starch granules be gelatinized. This is generally accomplished bythe action of heat while the material is in a moist state, and indeed,the gelatinization of starch and starchy flours under such conditions isfamiliar in culinary practice. It has been found that if starch isgelatinized in the presence of water, and subsequently dried, it maythen be readily dispersed in cold water without the necessity ofbringing the mixture to the initial gelatinized condition of the starch.Starches and starchy flours which have been so pre-gelatinized and driedto give a flaky or powdery product are well known and widely used forsuch diverse uses as Wallpaper pastes, infant cereals, oil well drillingmud additives, laundry starches, and the like.

Many of the uses of the type of product described require that theaqueous dispersion eventually prepared with the product must remainstable, that is, free from degradation by bacteria, molds, yeasts, andthe like, for 'a considerable length of time, and ideally, indefinitely.Thus, wall-paper paste should remain stable and undeteriorated forseveral days or weeks after being made, and the same is true for variousother glues and pastes made with a starchy base. The problem isparticularly acute when the product involved is a pre-gelatinized oilwell drilling mud starch, because in that case the stability must be ofindefinite duration or at least stable from 30 to 60 days, andpreferably more, because of the conditions of use. The quantitiesinvolved in a given usage where oil well drilling muds are involved arenormally very large, and premature spoilage of the starch additive mayentail the loss of thousands of dollars worth of drilling mud.

An object of the invention is to provide an oil well drilling mud starchwhich is pre-gelatinized and which is resistant to deterioration undernormal conditions of use.

An object of the present invention is to provide a process for making apre-gelatinized starch which is resistant to microbiologicaldegradation.

Other objects of the invention will appear as the description thereofproceeds.

In the drawings, FIGURE 1 shows an elevational view of a suitableapparatus to produce our novel material.

FIGURE 2 is a vertical section partly in elevation of the extruderportion of FIGURE 1.

FIGURE 3 is a sectional view taken as shown by the arrows in FIGURE 2.

FIGURE 4 is an enlarged detail View of the downstream end of theextruder.

Generally speaking, we pass a moist, raw, starchy flour containing anadmixture of between 1% to 5% by weight of paraformaldehyde and betweenabout 1% and 5% by weight of acompound having the following structuralformula:

m OH R; OH

where R and R are chosen from the group consisting of Cl and H, througha decreasing pitch extruder at a pressure of at least 200 lbs. persquare inch and at a temperature of at least 260 F., allowing the hotextruded starchy flour to expand downstream of said extruder and thendrying and grinding the product so obtained.

We use the term starch and starchy flour interchangeably, and mean toinclude the known and especially the commercially used starches andstarchy flours, particularly those which are rich in starch proper.These include com (maize), both ordinary and waxy; sorghum, bothordinary and waxy; potato; rice; tapioca; Brazilian arr-owroot; St.Vincents arrowroot; and less frequently encountered starches such asyuca, manioc, sago, barley, and the like. As stated, these may be usedin their flour form or in the relatively purified starch form.

The production of the starchy flour in accordance with the invention maybe better understood with reference to the drawings which show asuitable apparatus. Referring to FIGURE 1, this shows an extruder 10which is driven .by a motor 11 through suitable reduction gearing 12 anda flexible coupling 13.

The extruder 10 comprises a generally cylindrical housing made up offlanged sections, of which 15 is typical. Within the housing, the squareshaft 14 carries a worm screw, which is also sectional, 16 being atypical section. It will be observed from FIGURE 2 that, whereas theoutside diameter of the worm is constant, matching the inside diameterof the housing, the stock or shaft portion of the screw is of relativelysmall diameter at the input or feed end, which is at the left in FIGURE2, and tapers to a relatively large diameter at the output or right end.The free space between the stock of the worm screw and inner wall of thehousing thus becomes smaller as one goes from left to right in thesection shown in FIGURE 2.

At the same time, it will be observed that the pitch of the screwdecreases in going from left to right, that is, from the input to theoutput end. When a starchy flour is put into hopper 17, it falls downonto the worm screw at the point marked 18 at the extreme left of FIGURE2 and, when the screw is rotating, it is carried along by the screw fromleft to right at the same time it is compressed.

The worm screw is terminated on its right or output end, by a conicalcap 19, which fits with small clearance.

inside the final, or extruding section 20 of the housing. An opening forthe material is provided 'by an aperture 21 in a die plate 22.

The several sections 15 of the housing are each fitted with heatingmeans, preferably electric heaters, of which 23 and 24 are typical.While the extrusion process itself causes the material being worked uponto rise in temperature somewhat, it is not enough to maintaintemperature in the range required by the invention. The provision of amultiplicity of electric heaters as shown makes very precise temperaturecontrol possible.

An unexpected result of passing a starchy flour through an extruder inthe fashion described, whether the chemical preservatives hereinaboverecited are present or not. is that the product obtained is thinboiling, that is, when made into aqueous suspension, the viscosity ofthe suspension is much less than would be obtained from an equalconcentration of the original starchy flour, gelatinized by ordinarycooking. The alkaline fluidity of starchy flours in accordance with theinvention will range from 20 to as determined by the method which iswell standardized in the corn-wet milling industry. The quanpage 133 ofthe book Chemistry and Industry of Starch, second edition, by R. W.Kerr, New York: 1950. Five grams of the starchy material to be processed(dry basis) are stirred for one minute with 55 cc. of water, whereupon45 cc. of two normal caustic soda is added, followed by three minutesstirring. The mixture is then allowed to stand for 27 minutes at 25 F.,and is then poured into a standard fluidity funnel, which is a 4-inchdiameter, 60 glass laboratory funnel with the glass stem cut off andreplaced by a short glass tip adjusted so that 100cc. of water will flowout in 70 seconds. The alkaline fluidity is the volume in cc. of asolution of the starchy material prepared as just described which willflow out in 70 seconds. Unmodified starch will scarcely flow out at alland will have a fluidity of the order of 1 or 2.

The paraformaldehyde which we use in our invention is the ordinaryparaformaldehyde of commerce. The second compound, the structuralformula of which has already been given, may also be described inchemical terms as the following: (hydroxy, monoor dichlorophenyl)(hydroxy, monoor dichlorophenyl) sulfide.

We especially prefer that compound in accordance with the abovedescription and more particularly in accordance with the structuralformula given earlier in which the hydroxy groups are in the 2 positionthe chlorine atoms are both in the 4 posiiton, and the R and R are bothchlorine in the 6 position. This preferred compound which iscommercially available may thus be named as follows: bis(2-hydroxy 3,S-dichlorophenyl) sulfide.

We have found that both the formaldehyde and the chlorinated bis-phenolsulfide should be present each within the range of 1% to by weight ofthe dry starchy flour in order to be effective in accordance with the invention. The preferred and indeed the best admixture, considering all ofthe factors involved, is 3% by weight of paraformaldehyde and 3 byweight of the chlorinated bis-phenol sulfide and more particularly, ofhis (2-hydr0xy 3,5-dichlorophenyl) sulfide.

The processing of the starchy flour in the extruder in accordance withthis aspect of the invention may now be described in detail. Theparticle size of the starchy material is not especially critical; itshould merely be of convenient size to fall through the hopper and bepicked up by the rotating screw. Even when the starting material ismaize, the whole grains may be used in that state. They may also becracked and degerminated, if desired. If a dry-milled corn flour is usedto obtain a somewhat lower protein content, then it will of coursealready be in coarse powder form. Corn (maize) starch will necessarilybe quite fine as will the pure starches generally. Other grains such asrice may likewise be fed to the extruder whole, or cracked, or ground.Potato starch and potato flour are especially satisfactory for drillingmud use.

The moisture content of the starting material should be at least byweight, to allow suflicient water for gelatinizing and cooking. The bestmoisture content is approximately Moisture is expressed herein as thepercentage by weight of the whole material lost upon overnight drying at105 C. Where the supply of raw material is quite dry, it is well to addsufficient water to bring the moisture up to the figures just given, andallow some time for penetration of the added water into the interior ofthe grains or granules.

The paraformaldehyde and the chlorinated bis-phenol sulfide aregenerally obtained in dry, powdered form and may most conveniently beadded to the hopper along with the starchy flour. Of course, wheredesired, these two chemical additives may be admixed with the starchyflour some time prior to passing through the extruder.

The gelatinization process is simple and fast; the starchy material isfed into the hopper, taken up by the screw and simultaneouslycompressed, sheared, kneaded, and the like by the intensive mechanicalaction of the extruder, and, of course, heated. The material reachingthe final section 10 of the extruder will be at a temperature of between260 F. and 330 F., and at a pressure of at least 200 p.s.i. (pounds persquare inch). As it exits from the die plate, the pressure is suddenlyreleased to atmospheric, and a flash expansion of the superheated waterin the material leads to a considerable enlargement in cross-sectionaldiameter, as indicated in FIGURE 4. In a very short time, the extruded,puffy mass will have dried and cooled enough to be relatively solid.

Depending upon the factors of moisture content of feed, extrusiontemperature, and kind and nature of the starchy material, and also ofcourse upon the ambient humidity and temperature, the extruded mass maybe allowed to air dry or it may be artificially dried by suitableordinary chemical process equipment, and then ground, as in a hammermill, to produce a product in convenient form for treatment of a mudfluid, or for wall-paper paste or whatever end use is desired.

As has been mentioned, an especially important use for the degradationresistant pre-gelatinized starchy flours of the present invention is inconnection with rotary drilling mud fluids. In the drilling of wells insearch of oil and gas by the rotary method, a drilling fluid or made iscirculated downwardly through a continuous string of drill pipe, issuingat the bit through ports provided therein. The drilling fluid thencirculates upwardly through the cylinder of the annular cross-sectionformed between the exterior of the drill pipe, and a more or lesscorresponding amount flows out at the top of the well, exterior to thedrill pipe. The outfiowing mud may be passed through ditches, screensand the like to remove impurities and may be conditioned by variouschemical and mechanical treatments so as to keep it suitable for itspurpose, and it is then taken up by mud pumps and recirculated back downinto the drill pipe. The circulation of the drilling fluid issubstantially continuous during a given session of drilling. When thedrill pipe is withdrawn from the hole in order to change bits and thelike, the drilling fluid remains in the hole.

In nearly all cases, wells drilled for oil and gas penetrate sedimentaryformations which will expose strata of varying degrees of porosity andpermeability to the well bore. Drilling fluids of the type underconsideration here contain finely divided mineral matter, which in anycase will have been derived from the process of drilling up formation inorder to make the well bore; and, in most casses additionally willcontain such material as a result of deliberate addition of clays andother finely divided minerals such as limestone, barite, hematite, andthe like.

Now a fundamental difliculty which is almost uni versally encountetredis that the drilling fluid or mud undergoes filtration at the walls ofthe bore hole opposite porous formations. In the ordinary case, thefiltration consists of the liquid proper of the drilling fluid leavingthe bore hole and entering the porous formation or stratum, leavingbehind as a filter cake on the wall of the bore hole a sludge of thesolid matter of the drilling fluid together with some of the liquid.This tends to take place for the reason that the drilling fluid isalways maintained, or at least when good drilling practice is carriedout, should be maintained, so that is exerts a hydrostatic pressureagainst porous formations which is samewhat greater than the pressure ofany fluids contained in the formation. If this is not done, then highpressure fluids will intrude into the bore hole and may lead to the lossof the well, particularly when the fluid in question is gaseous.

It is necessary to maintain the mud in such a condition that theformation of a filter caket as describetd is kept at an absolutetminimum. Where the drilling mud is of a water-base type it is common toadmix theretwith a water-soluble or water-dispersible hydrophiliccolloid, so that the colloid disperses therein and is made to in teracttherewith. Natural gums, such as karaya, have been used, and alsostarches and starchy flours. These are subject to microbiologicaldegradation, unless suitably treated, chiefly by bacteria, yeasts, andmolds, 'so that there is some usage of completely synthetic polymerssuch as sodium carboxymethylcellulose and sodium polyacrylate. Suchsynthetic polymers appear to be relatively resistant to degradation, sothat they find a use in drilling muds even in spite of their much highercost when compared with starches, since they can be added to otherwiseuntreatetd mud. However, the starchy flour products made in accordancewith our invention are quite as resistant to degradation whenincorporated with drilling muds as are the much more expensive syntheticpolymers of the type just described. Their use therefore is asignificant advance in drilling mud technology. They may be employed inthe same range of proportions as is common with pre-gelatinized starchand starchy flours. This is the range of /2 lb. to 25 lbs. per barrel(42 U8. gallons) of the mud which is treated. The fluid loss of the mud'so treated will be reduced quite as Well and in most cases even betterthan by the employment of the same weight of starch or starchy flourwhich does not contain the two chemical additives already disclosed. Asalready mentioned, the starchy flours proc essed through the extruder inaccordance with our invention as disclosed will have an alkalinefluidity within the range of 20 to 70.

Some examples of proceeding in accordance with the invention will now begiven:

Example 1 Potato starch from Colorado, which had a moisture content of17%, was treated with water to give a moisture content of 25% and 2% byweight of paraformaldehyde and 3% by weight of bis (Z-hydroxy,3,5-dichlorophenyl) sulfide were added. This was then passed through anextruder as shown in the drawings with a barrel length of 72 inches anda compression ratio of 4.5 to 1, with /z-inch orifice, at 260 F. and 500lbs. per square inch, measured just upstream from the orifice. Theextruded material was allowed to air dry, and was then ground in ahammer mill. It readily dispersed in water at room temperature, and wasusable as a paper paste, without further treatment. Water suspensionswere stable for at least a 3-week duration of the observation. Whenadded to a drilling fluid which consisted of water, a natural shale,some bentonite, and some ferrochrome lignosulfonate, an addition of 3.5lbs. per barrel gave a fluid loss reduction from 56 cc. to 6 cc. Thismud was stable, without evidence of deterioration, for the threeweekduration of the test.

Example 2 Corn (maize) starch and tapioca starch were separatelyprocessed as set forth in Example 1 hereinabove, except that themoisture content was adjusted to 19% for the corn starch and 23% for thetapioca starch, prior to passing the mixture through the extruder; andalso except that the percentage of paraformaldehyde 'was 3% in eachcase. Excellent products were obtained, which exhibited very goodstability when tested in a mud consisting of approximatetly 4%attapulgite dispersed in a 10% aqueous sodium chloride solution, andsaturated with gypsum. The filter loss of the test mud was well over 50ml. A.P.I. before the addition of the starches processed in accordancewith the invention. When the latter were added at a concentration of 3.5lbs. per barrel, the filter loss was reduced as follows:

The viscosities of the treated muds were both quite low, andsatisfactorily pumpable.

Example 3 Potato starch was processed in accordance with the inventionin a large, production-size extruder essentially similar to that shownin the drawings; the worm diameter was 8 inches, and the extruder properhad a length of 11 feet, 10 inches. The downstream sections of theextruder were maintained at a temperature between 260 F. and 305 F., andthe pressure varied between 400 and 800 psi. The throughput rate was1200 lbs. per hour on a continuous basis; the moisture content of thefeed was 24.5%, and that of the product as 12%. The worm was rotated at108 rpm.

When the product was tested in the mud described in Example 2, at thesame concentration, the following results were obtained:

Initial filtrate, API 11.6 Filtrate after 16 hrs. rolling at 150 9.9

While our invention has been illustrated in terms of and with the aid ofspecific examples, it will be understood that various modifications andchanges may be made in proportions, details of procedure, and the like,all within the broad scope of the invention as defined in the claimsthat follow:

Having described the invention, we claim:

1. In a process for drilling a well by the rotary method wherein awater-base drilling fluid is circulated in said well, the method ofcontrolling the formation of a filter cake on the wall of said wellwhich comprises admixing with said drilling fluid and interactingtherewith a gelatinized starchy flour product which has been produced bycombining a moist starchy flour containing from 1% to 5% by weight ofparaformaldehyde and from 1% to 5% of a compound having the formula:

where R and R are chosen from the group consisting of Cl and H, andextruding said flour at a pressure of at least 200 lbs. per square inchand at a temperature of at least 260 F., allowing the hot, extrudedstarchy flour to expand at atmospheric pressure after said extrusion,and drying and grinding the product so formed, in an amount sufficientto lower the fluid loss of said drilling fluid but insuflicient toincrease the viscosity of said fluid to such an extent to render saiddrilling mud uncirculatable.

2. The process in accordance with claim 1 in which said compound is his(2-hydroxy, 3,5-dichlorophenyl) sulfide. 3. The process in accordancewith claim 1 wherein said compound is his (2-hydroxy,3,5-dichlorophenyl) sulfide and said product is admixed with saiddrilling fluid in an amount within the range of /2 to 25 lbs. per barrelof said fluid.

References Cited by the Examiner UNITED STATES PATENTS 2,353,735 7/1944Kunz 252-107 2,417,307 3/1947 Larsen 252- 2,908,597 10/1959 Owen 127-713,137,592 6/ 1964 Protzman et al 127-71 LEON D. ROSDOL, PrimaryExaminer.

H. B GUYNN, Assistant Examiner.

1. IN A PROCESS FOR DRILLING A WELL BY THE ROTARY METHOD WHEREIN AWATER-BASE DRILLING FLUID IS CIRCULATED IN SAID WELL, THE METHOD OFCONTROLLING THE FORMATION OF A FILTER CAKE ON THE WALL OF SAID WELLWHICH COMPRISES ADMIXING WITH SAID DRILLING FLUID AND INTERACTINGTHEREWITH A GELATINIZED STARCHY FLOUR PRODUCT WHICH HAS BEEN PRODUCED BYCOMBINING A MOIST STARCH FLOUR CONTAINING FROM 1% TO 5% BY WEIGHT OFPARAFORMALDEHYDE AND FROM 1% TO 5% OF A COMPOUND HAVING THE FORMULA: